1. Field of the Invention
The invention relates to radioactive therapeutic seeds. More particularly, the invention relates to improved radioactive therapeutic seeds for the treatment of oncological and other medical conditions.
2. State of the Art
Radioactive seed therapy is a well known and well accepted medical procedure for the treatment of various oncological and other medical conditions. Seed therapy, also known as brachytherapy typically involves the implantation of fifty to one hundred tiny capsules (seeds) into or around a treatment site. The capsules contain a radioactive isotope which irradiates the treatment site at close range without adversely affecting other parts of the body. Brachytherapy has been used successfully in the treatment of various types of cancers such as prostate cancer. It has also been used to prevent the growth or regrowth of tissues in the treatment of various occlusive diseases such as arteriosclerosis and arthrosclerosis subsequent to balloon angioplasty.
Radioactive therapeutic seeds are carefully designed to possess several important qualities. First, they are relatively small, typically approximately 0.025 inch in diameter and approximately 0.16 inch long so that they may be implanted using minimally invasive instruments and techniques. Second, the radioactive isotope must be enclosed in a biocompatible protective package since the seeds are typically not removed and will remain in the body for many years. Third, each seed preferably includes a radiopaque (e.g. high Z material) marker so that it can be located at the treatment site with the aid of fluoroscopy. Fourth, the protective package and the radiopaque marker preferably do not cast xe2x80x9cshadowsxe2x80x9d in the irradiation pattern of the isotope. Fifth, the isotope should be evenly distributed within the protective package so as to avoid any xe2x80x9chot spotsxe2x80x9d of radiation.
The state of the art of radioactive therapeutic seeds is substantially disclosed in several co-owned patents to Slater et al. including U.S. Pat. Nos. 6,007,475, 6,066,083, 6,080,099, 6,200,316, 6,210,316 as well as eight additional U.S. Pat. No. 6,099,458 to Robertson for xe2x80x9cEncapsulated Low-Energy Brachytherapy Sourcesxe2x80x9d, U.S. Pat. No. 5,713,828 to Coniglione for xe2x80x9cHollow-Tube Brachytherapy Devicexe2x80x9d, U.S. Pat. No. 5,405,309 to Carden, Jr. for xe2x80x9cX-Ray Emitting Interstitial Implantsxe2x80x9d, U.S. Pat. No. 4,891,165 to Suthanthiran for xe2x80x9cDevice and Method for Encapsulating Radioactive Materialsxe2x80x9d and U.S. Pat. No. 4,784,116 to Russell, Jr. et al. for xe2x80x9cCapsule for Interstitial Implantsxe2x80x9d, U.S. Pat. No. 4,702,228 to Russell, Jr. et al. for xe2x80x9cX-Ray Emitting Interstitial Implantsxe2x80x9d, U.S. Pat. No.4,323,055 to Kubiatowicz for xe2x80x9cRadioactive Iodine Seedxe2x80x9d, and U.S. Pat. No. 3,351,049 to Lawrence for xe2x80x9cTherapeutic Metal Seed Containing within a Radioactive Isotope Disposed on a Carrier and Method of Manufacturexe2x80x9d.
The Lawrence patent describes many of the essential features of radioactive therapeutic seeds. Lawrence describes radioactive isotopes (I-125, Pd-103, Cs-131, Xe-133, and Yt-169) which emit low energy X-rays and which have relatively short half-lives. When implanted at a treatment site, these isotopes provide sufficient radiotherapy without posing a radiation danger to the medical practitioner(s), people in the vicinity of the patient, or other parts of the patient""s body. Lawrence further describes a protective capsule which contains the isotope and prevents it from migrating throughout the body where it might interfere with healthy tissue. The capsule is cylindrical and made of low atomic number biocompatible materials such as stainless steel or titanium which substantially do not absorb X-rays. The isotope is coated on a rod shaped carrier made of similar X-ray transparent (e.g. low Z) material and is placed inside the capsule cylinder. The ends of the capsule cylinder are closed by swaging or spinning and soldering or welding. According to a preferred embodiment, Lawrence places a radiopaque marker inside the seed. In one embodiment, the marker is a wire embedded inside the carrier rod. The wire is made of high atomic number material such as gold or tungsten which absorb X-rays.
In 1980, Kubiatowicz made a minor improvement in the basic Lawrence design by providing that the entire isotope carrier be made of radiopaque material such as silver. Kubiatowicz recognized that since the isotope was carried on the entire outer surface of the carrier, there was no need to make the carrier body X-ray transparent as suggested by Lawrence. The larger radiopaque carrier body described by Kubiatowicz makes the seeds easier to see with X-ray or fluoroscopic examination. Thus, the seeds may be placed more accurately at or around the treatment site.
Several years later, Russell, Jr. et al., in U.S. Pat. Nos. 4,707,228 and 4,784,116, explained that the capsule design of Lawrence and Kubiatowicz produces anisotropic angular radiation distribution. According to Russell, Jr. et al., the shell forming techniques used in the Lawrence-type seeds results in large beads of shell material at the ends of the seeds. These beads substantially shield radiation thereby casting shadows in the irradiation pattern of the isotope. Russell, Jr. et al. proposed a new seed design to solve this problem. In particular, Russell, Jr. et al. proposed a seed having a cylindrical container which is sealed with end caps which have a wall thickness that is substantially the same as the wall thickness of the cylindrical container. The end caps are attached to the cylindrical container by welding or crimping.
An alternate solution to the non-uniform radiation pattern of the Lawrence type seeds was proposed by Suthanthiran in U.S. Pat. No. 4,891,165. Suthanthiran""s solution was to form a seed capsule from two interfitting sleeves, each having one open end and one closed end. The thickness of the sleeve side walls and their closed ends is such that when the sleeves are interfit in an overlapping manner, the total side wall thickness of the assembled capsule is approximately equal to the end wall thickness.
Other improvements in radioactive therapeutic seeds are disclosed in U.S. Pat. No. 5,405,309 which concerns a safe isotopically pure Pd-103 seed, U.S. Pat. No. 5,713,828 which discloses a hollow tube seed which can be implanted with suture material, and U.S. Pat. No. 6,099,458 which discloses a seeds which are manufactured in a simplified manner which includes placing sources in titanium capsule halves, providing a titanium plug having a marker therein internal the capsule halves, and welding the titanium capsule halves to the titanium plug.
Despite the fact that radioactive therapeutic seeds have been in use for over thirty years and despite the several significant improvements made in these seeds, many concerns still exist regarding their design and construction. For example, while significant attention has been given to the methods by which a cylindrical seed capsule is sealed, it is still difficult to seal such a small cylindrical capsule without adversely affecting the functionality of the seed. Most capsules are sealed at an end using solder which causes a shadow and consequent anisotropic radiation distribution, and while the U.S. Pat. No. 6,200,258 to Slater et al., and U.S. Pat. No. 6,099,458 to Robertson overcome some of these problems, they still suffer from issues regarding thick plugs of titanium around the markers which can affect the isotropic distribution of radiation.
It is therefore an object of the invention to provide radioactive therapeutic seeds which have a relatively isotropic radiation pattern.
It is also an object of the invention to provide radioactive therapeutic seeds which are easy to manufacture.
It is another object of the invention to provide radioactive therapeutic seeds which can be deployed relatively quickly and easily.
In accord with these objects which will be discussed in detail below, the radioactive therapeutic seeds of the present invention include a substantially radiotransparent cylindrical capsule containing a radioactive isotope and preferably a radiopaque marker. Each of the embodiments is designed to provide a substantially isotropic distribution of radiation. As used herein, the terms xe2x80x9cradiotransparentxe2x80x9d, xe2x80x9cradiolucentxe2x80x9d, xe2x80x9cradiotranslucentxe2x80x9d, and xe2x80x9clow Z materialxe2x80x9d are used interchangeably.
According to a first embodiment of the invention, the isotope is deposited on the outer surface of a hollow radiolucent tube and a ceramic collar having a metal ring centrally located thereon is preferably tightly fit about a central portion of the tube. The capsule comprises two tubular halves, each having a closed end and an open end. The halves of the capsule are positioned over the tube with the open ends of the halves being interference fit with the collar and abutting the metal ring. The capsule halves, typically formed of titanium, are welded to the ring (also typically formed of titanium) to seal the capsule. The ceramic collar protects the contents of the capsule from the heat of welding and is even more radiotransparent than the titanium, and therefore does not affect the radiation pattern of the seed.
According to a second embodiment of the invention, the isotope bearing structure may be one or more radiolucent particles, preferably made from titanium, aluminum or glass, and preferably spherically shaped. The particles are provided with a thin coating of silver to facilitate the adhesion of the isotope thereto. Also provided is a tubular ceramic spacer having an axial radiopaque marker therein and a titanium ring thereon. The titanium ring provides a surface to which the open ends of the two halves of the capsule are butt against and welded.
According to a third embodiment of the invention, the isotope bearing structure is preferably a pair of silver tubes having outer and inner surfaces on which the isotope is provided. One silver tube is positioned in each half of the capsule, and the halves of the capsule are welded about a titanium ring which is fit over a centrally located tubular ceramic spacer. The spacer is preferably provided with a radiopaque marker therein. In addition, the isotope bearing tube is preferably smaller than the interior of each half of the capsule, and additional spacers are preferably provided in each half of the capsule between the tube and the ceramic spacer to prevent relative movement of the tube within the capsule.
In each of the first three embodiments, it is preferred that the ring surrounding the ceramic spacer be made of the same material as the walls of the capsule halves. Depending upon the process of joining the capsule halves, the ring may be the same thickness as the walls of the capsule halves or may have a slightly greater thickness (e.g., up to 0.005 inches thicker) than the capsule halves so that the ring stands proud of the capsule halves, provided that after joining the capsule halves together, the ring is substantially flush with (within a few thousands of an inch) the capsule halves. In addition, in each of the first three embodiments it will be appreciated that the halves of the capsule do not overlap each other and the configuration of the capsule, isotope, and ceramic spacer or collar provide the seed with a highly isotropic distribution of radiation.
According to a fourth embodiment of the invention, the isotope bearing structure may be one or more radiolucent particles, preferably made from titanium, aluminum or glass, and preferably spherically shaped. The particles are preferably provided with a thin coating of silver to facilitate the adhesion of the isotope thereto. Also provided is a tubular ceramic spacer having an axial radiopaque marker therein. The tubular ceramic spacer and radiopaque marker may each be formed from one or two pieces. Where the tubular ceramic spacer and radiopaque marker are formed from two pieces, a first spacer with a first marker therein is press fit into an open end of a first half of the capsule, while a second spacer with a second marker therein is press fit into an open end of a second half of the capsule. The first and second halves of the capsule are then abutted and welded. Where the ceramic spacer and radiopaque marker are each formed from one piece, the spacer, with the marker therein, is press fit partially into the open end of a first half of the capsule, and the open end of the second half of the capsule is then press fit over the remainder of the spacer to abut the first half of the capsule. The two capsule halves are then welded. Alternatively, the open ends of the capsule halves may be thinned and the open end of the second capsule half may be forced over the open end of the first capsule half. The capsule halves may then be joined by welding, swaging, or other means.
Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures.